iwlwifi: mvm: add switch_vif_chanctx operation

Implement the switch_vif_chanctx operation with support for a
single-vif and SWAP mode.  The REASSIGN mode and multi-vifs are not
supported yet.

This operation needs to implement 4 steps, namely unassign, remove,
add and assign the chanctx.  In order to do this, split out these
operations into locked and non-locked parts, thus allowing us to call
them while locked.

Additionally, in order to allow us to restart the hardware when
something fails, add a boolean to the iwl_mvm_nic_restart() function
that tells whether the restart was triggered by a FW error or
something else.

Signed-off-by: Luciano Coelho <luciano.coelho@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>